1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a mechanism for processing location information.
2. Description of Related Art
Wireless communication is an increasingly popular means of communication in the modern world. People are using wireless networks for the exchange of voice and data as an alternative to using a wired infrastructure. In principle, a user can seek information over a packet data network such as the Internet or call anyone over a public switched telephone network (PSTN) from any place inside a coverage area of a wireless network.
In a typical wireless network, an area is divided geographically into a number of cell sites, each defined by one or more radiation patterns created by an emission of radio frequency (RF) electromagnetic waves from a respective base transceiver station (BTS) antenna. For wireless communications, RF signals are not sent through a transmission line and, therefore, antennas are required for the transmission and reception of the signals.
Unfortunately, however, buildings, tunnels, land masses, or other areas that block RF signals may obstruct the transmission and reception of RF signals. To overcome this problem, a distributed antenna system (DAS) may be used to bring RF coverage inside and throughout a facility, underground (for example, within tunnels), or anywhere that outdoor RF signals do not reach.
A DAS may comprise, for example, any network of components that receives an input RF signal, converts it to a wired signal (e.g. electrical, optical, etc.) or another wireless media, transports it throughout a facility, and then re-converts it back to an RF signal for transmission inside the facility. By way of example, a DAS may comprise multiple antennas positioned throughout a building (or other RF-blocked areas), interconnected through remote hubs using fiber-optic cables. The DAS may also include a distributed antenna system controller (DASC) connected to the remote hubs using, for example, fiber-optic cables. The DASC receives wireless signals from a BTS and converts the wireless signals into optical signals. The fiber optic cables then distribute the optical signals from the DASC to the remote hubs, which send the signals to the antennas throughout the building. The antennas receive the optical signals and convert them back to RF signals for wireless transmission inside the building. In addition to communications functionality, mobile stations (such as cellular telephones) can provide location information. For example, a cellular telephone with GPS functionality may provide a network or a user of the telephone with coordinates of the current location of the mobile station. Additionally, in wide-area (not in-building) cellular networks, a mobile station can be located by location triangulation using angle of arrival (AOA) and/or time difference of arrival (TDOA).
The usefulness of these systems is less than promising at an in-building setting (or within a set of buildings). GPS, for example, has significant signal attenuation because of building structures and, in addition, does not have multi-floor functionality. In a multi-floor building, such as a high-rise building, for instance, GPS cannot accurately distinguish between the location of a first device on a first floor and the location of a second device on a second floor.
AOA and TDOA involve complex calculations and more specialized network equipment. Further, due to the nature of indoor environments, AOA technology cannot be used reliably to compute the position of a mobile station. Signal reflection, for example, can create significant problems for an indoor AOA system. Also, TDOA technology requires very fine grained time synchronization between the transmitter and receiver, which is not feasible with current off-the-shelf mobile devices.